Exposure to sunlight and other sources of ultraviolet radiation is known to cause degradation of a variety of materials, especially polymeric materials. For example, polymeric materials such as plastics often discolor and may become brittle as a result of exposure to ultraviolet light. Accordingly, a large body of art has been developed directed towards materials such as ultraviolet light absorbers and stabilizers that are capable of inhibiting such degradation.
A class of materials known to be ultraviolet light absorbers are o-hydroxyphenyltriazines, in which at least one substituent on the 1, 3, or 5 carbon of the triazine ring is a phenyl group with a hydroxyl group ortho to the point of attachment to the triazine ring. In general this class of materials is well known in the art.
For example, U.S. Pat. No. 3,843,371 discloses hydroxyphenyltriazines for use in photographic materials.
U.S. Pat. No. 3,896,125 discloses hydroxyphenyl triazines light stabilizers for organic polymeric substrates.
The use of hydroxyphenyltriazines alone or in combination with other light stabilizers such as hydroxyphenylbenzotriazoles, benzophenones, oxanilides, cyanoacrylates, salicylates, and hindered amine light stabilizers (HALS), for the stabilization of polymers is also well known. For example, U.S. Pat. Nos. 4,853,471, 4,921,966, 4,973,701, and 4,973,702 disclose such combinations.
Typically, the aforementioned aryl ring with the hydroxyl group ortho to the point of attachment to the triazine ring is based on resorcinol and, consequently, this aryl ring also contains a second substituent (either a hydroxyl group or a derivative thereof) para to the point of attachment to the triazine ring. For example, U.S. Pat. Nos. 3,118,837 and 3,244,708 disclose p-alkoxy-o-hydroxyphenyl triazines with improved UV protection.
This para-substituent can be “non-reactive,” as in the case of an alkyloxy group, or “reactive” as in the case of a hydroxyalkyloxy (active hydrogen reactive site) or (meth)acryloyl (ethylenic unsaturation reactive site) group. For the purposes of the present invention, the former are referred to as “non-bondable” triazines and the latter are referred to as “bondable” triazines.
Low volatility is an important characteristic of stabilizers used in any applications where high, temperatures are encountered. High temperatures are used in the processing of thermoplastics and in the curing of thermoset resins and coatings. High temperatures are also often present in the end-use applications of the stabilized material. Low volatility will prevent loss of the stabilizer during processing, curing, and high temperature end-uses. Besides reducing losses of stabilizer during processing or curing, low volatility will minimize processing problems such as die lip build-up and plate-out.
Many polymer additives (such as ultraviolet light stabilizers) migrate out of the polymer substrate to be protected, or are adsorbed (chemically or physically) by one or more systems components (such as pigments), thereby diminishing their effectiveness. Such migration and adsorption problems are examples of the general problems of lack of solubility and compatibility found for many commercial polymer additives.
Bondable triazines are well known in the art. For example, U.S. Pat. Nos. 3,423,360, 4,962,142, and 5,189,084 disclose various bondable triazines and the incorporation of these compounds into polymers by chemical bonding. Bondable stabilizers have a potential advantage in that, depending on the bondable functionality and the particular polymer system to be stabilized, they can be chemically incorporated into a polymer structure via reaction of the bondable functionality either during polymer formation (such as in the case of polymerizing monomers or a crosslinking polymer system) or subsequently with a preformed polymer having appropriate reactive functionality. Accordingly, due to such bonding, migration of these UV absorbers between layers of multi-layer coatings and into polymer substrates is greatly reduced.